Open circuit potential, OCP

Some metals are thermodynamically unstable in aqueous solutions because their equilibrium potential is more negative than the potential of the reversible hydrogen electrode in the same solution. At such electrodes, anodic metal dissolution and cathodic hydrogen evolution can occur as coupled reactions, and their open-circuit potential (OCP) will be more positive than the equilibrium potential (see Section 13.7). 

An EG G PARC 273 Potentiostat/Galvanostat was used in both the electrolysis and the CV experiments, coupled with an HP 7044B X/Y recorder. A Solartron 1255 HF Frequency Response Analyzer and a Solartron 1286 Electrochemical Interface were employed for the a.c. impedance measurements, using frequencies from 0.1 to 65 kHz and a 10 mV a.c. amplitude (effective) at either the open circuit potential (OCP) or at various applied potentials. As the RE can introduce a time delay at high frequencies, observed as a phase shift owing to its resistance and capacitance characteristics, an additional Pt wire electrode was placed in the cell and was connected via a 6.8 pF capacitor to the RE lead [32-34]. 

The dissolution of PS during PS formation may occur in the dark or under illumination. Both are essentially corrosion processes, by which the silicon in the PS is oxidized and dissolved with simultaneous reduction of the oxidizing species in the solution. The material in the PS, which is distant from the growing front is little affected by the external bias due to the high resistivity of PS and is essentially at the open circuit potential (OCP). Such corrosion process is responsible for the formation of micro PS of certain thickness (stain film) in HF solutions containing oxidants under an unbiased condition. 

Aqueous electrolytes of high pH etch silicon even at open circuit potential (OCP) conditions. The etch rate can be enhanced or decreased by application of anodic or cathodic potentials respectively, as discussed in Section 4.5. The use of electrolytes of high pH in electrochemical applications is limited and mainly in the field of etch-stop techniques. At low pH silicon is quite inert because under anodic potentials a thin passivating oxide film is formed. This oxide film can only be dissolved if HF is present. The dissolution rate of bulk Si in HF at OCP, however, is negligible and an anodic bias is required for dissolution. These special properties of HF account for its prominent position among all electrolytes for silicon. Because most of the electrochemistry reported in the following chapters refers to HF electrolytes, they will be discussed in detail. 

Paunovic (31) studied the induction period for the overall process, dividing it into dependence of the open-circuit potential (OCP) on the oxidation and reduction... 

In the positive branch of the i/V graph, anodic dissolution process will remove material from silicon crystals. The conditions for optimal etching of silicon have been extensively explored for micromachining or surface polishing in the fabrication of electronic devices. Most generally, the etch rate of silicon in HE solutions is isotropic among the various crystalKne orientations. The etch rate of silicon at room temperature at the open-circuit potential (OCP) is very low, on the order of 10 nm s , which is equivalent to 100 nA cm , in aqueous HE solutions. 

The rate of the reoxidation of Mg deposits is controlled by their morphology, which in turn depends on the substrate material. Smooth and compact deposits were obtained using silver or gold, but not nickel or copper. It was also established that the open circuit potential (OCP) of magnesium electrode (a fresh deposit on a Pt) in concentrated solutions of 5 depends strongly on the solvent used. In THE solutions with c around 1 M at 22 °C under argon atmosphere, the values of OCP for 5a, 5b and 5f were equal to —2.8, —2.73 and —2.77 V vs. Ag+/Ag, respectively-. ... 

Measurements of the open circuit potential (OCP) were performed by linear sweep voltammetry with the anode of the electrolyser set as the working electrode, and the cathode set as both counter and reference electrodes. The hydrogen reference electrode condition was created by saturating the catholyte with H2 gas at the room temperature. The measured OCP values were refered to the standard hydrogen electrode (SHE). Since the potential of the hydrogen reference electrode varied from SHE depending on the HC1 concentration used in the experiement, this correction was taken into account for all measured OCP. 

Experimental values of the open circuit potential (OCP) measured by linear sweep voltammetry using the newly developed CuCl/HCl electrolyser were found to be consistent with the theoretical thermodynamic calculations. The performed electrolysis tests over wide ranges of temperature demonstrated that the elevated temperatures enhance the system performance. The current efficiency of the CuCl/HCl electrolyser, estimated using the amount of produced hydrogen, at current densities below 100 mA was found to be above 90% for a number of tested commercially available membranes. The current efficiency at current density above 100 mA was reduced mainly due to permeation of Cu through the membranes. 

Open-circuit potential (OCP) — This is the - potential of the - working electrode relative to the - reference electrode when no potential or - current is being applied to the - cell [i]. In case of a reversible electrode system (- reversibility) the OCP is also referred to as the - equilibrium potential. Otherwise it is called the - rest potential, or the - corrosion potential, depending on the studied system. The OCP is measured using high-input - impedance voltmeters, or potentiometers, as in - potentiometry. OCP s of - electrodes of the first, the second, and the third kind, of - redox electrodes and of - ion-selective membrane electrodes are defined by the - Nernst equation. The - corrosion po-... 

Thus, no passivating layer is formed due to the fact that silicon dissolves in such media. Therefore, the anodic I-V curve of silicon in HF is quite unique and differs from the I-V curves obtained in acidic (HF-free) and alkaline electrolytes. Less attention has been paid to the electrochemistry of silicon in alkaline electrolytes as compared to the study of the electrochemistry of silicon in acidic electrolytes, probably due to the fact that pore formation is observed only in acidic media. In contrast to acidic solutions, silicon dissolution occurs in alkaline solutions under - open circuit potential (OCP). 

In the study described in this review article, electrochemical experiments were hmited to open-circuit potential (OCP) measurements, cychc voltammetry (CV), and potential-dependent dissolution. 

The electrodeposition of gold was made in an acidic electrolyte of 0.005 M HAUCI4 per liter. The open circuit potential (OCP) after deposition was +820 mV versus SCE. The pulse potentials were varied between +800 and +600 mV versus SCE. Particles between 10 and 500 nm diameter were prepared. 

Fig. 5 shows the volume of the wear track in 0.5 M H2SO4 solution versus applied (or free) potential. One can observe from the figure that wear is negligible when a cathodic potential (- 0.9 V versus Ag / AgCl) is applied. At open circuit potential (OCP) some wear is measured and at an applied anodic potential the wear track volume is increasing as applied anodic potential is increased. These results suggest that the formation of oxide is indispensable to the wear process and that the wear rate is related to the oxide formation. 

Figure 2 Cu Polish rate as a function of glycine concentration Figure 4 shows the copper dissolution rate as a function of H2O2 concentration in the presence of 1 wt % glycine. The variation in the open-circuit potential (OCP) measured with respect to SCE at KXK) rpm rotational speed, as measured in an ex situ electrochemical corrosion cell, is also plotted as a function of H2O2 concentration. The copper dissolution rate decreases with increasing peroxide concentration, which is contrary to the expectation. If copper...

The power efficiency of a photoelectrode ean be eharaeterized by the open-circuit potential (OCP) and short-circuit current ... 

As the most easily measurable electrochemical parameter, the open-circuit potential (OCP) is routinely used to indicate the condition, stability, and reproducibility of an electrode during experiments. Table 2.16 shows the OCP values of silicon electrodes in various electrolytes. 

The equilibrium electrode potential is the electrical potential of an electrode measured against a reference electrode when there is no current flowing through the electrode. It is also called open circuit potential (OCP). The equilibrium potential between a metal and a solution of its ions is given by the Nernst equation as follows ... 

Instrument Company). The current was recorded on a x-y recorder as a function of potential applied to the working electrode with respect to the reference electrode. In most CV experiments the potential sweep rate was 0.1 V per second. No potential was applied to the working electrode right after the contact was made between the Ni(lll) working electrode and the electrolyte to avoid possible electrochemical reactions before the potential sweeping was begun. The open-circuit potential (OCP) was always measured first, then the potential sweep was initiated from the... 

The open-circuit potential (OCP) recorded immediately after bringing in contact the C0-c(4x2)/Ni(lll) specimen with the 0.1 M KOH electrolyte was found to be about 0.24 V vs DHE (The electrode potential of Che DHE in 0.1 M KOH vs Reversible Hydrogen Electrode (RHE) was calculated to be 0.06 V. All of the electrode potentials in this thesis are cited vs DHE)) drifting rapidly over about 2 minutes to a fairly stable value of 0,20 V. This behavior was found to be very reproducible, yielding for... 

The most straightforward interpretation of the open-circuit potentials (OCP) is as followsio ... 

A three-electrode cell was used for the electrochemical impedance measurements, consisting of the working electrode, a platinum counter electrode, and a saturated calomel electrode (SCE). The electrolyte was 0.1 M sodium chloride. A Zahner-Electric IM6d impedance spectrometer was used for the impedance measurements. The impedance spectra were recorded at open circuit potential (OCP) in a frequency range from 0.1 Hz to 50 kHz with an AC amplitude of 10 mV. The thickness of the barrier film was calculated from the capacitance, a dielectric constant of 6.5 estimated from electrical measurement (see below) was used. 

The aluminium oxide films formed for different times (marked in Figure 23.10) were characterised by electrochemical impedance spectroscopy. For the aluminium oxide film anodised for 160 s, the open circuit potential (OCP) is not stable. This can be explained by instability of the film structure. The processes of the film formation were not yet completed. The OCP is more stable and positive for films anodised for more than 700 s. This can be explained by the formation of the compact barrier aluminium oxide layer. 

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